Current flow controller

Abstract

A current flow controller ( 10 ) comprising: a plurality of terminals ( 12 a, 12 b, 14 a, 14 b ) for connection, in use, to a plurality of DC power transmission medium ( 16,18 ) such that each DC power transmission medium ( 16,18 ) is connected to at least one of the plurality of terminals ( 12 a, 12 b, 14 a, 14 b ); and a current flow control unit interconnecting the plurality of terminals ( 12 a, 12 b, 14 a, 14 b ), the current flow control unit including a plurality of current flow control sub-units ( 20, 22, 23 ) each of which is, in use, connected to a respective DC power transmission medium ( 16, 18 ), each current flow control sub-unit ( 20, 22, 23 ) including at least one switching element ( 24, 28 ), the or each switching element ( 24, 28 ) of each current flow control sub-unit ( 20, 22, 23 ) being connected to the same energy storage device ( 26; 56 ) to selectively provide a voltage source, and a switching control unit ( 100 ) to control switching of each switching element ( 24, 28 ) of the current flow control unit to selectively inject a voltage drop (V 1 , V 2 ), in use, into each DC power transmission medium ( 16,18 ) so as to simultaneously regulate current flow (I 1 , I 2 ) in each DC power transmission medium ( 16, 18 ) and divert energy from at least one DC power transmission medium ( 16, 18 ) into at least one other DC power transmission medium ( 16, 18 ) via the current flow control unit.

The invention claimed is: 
     
       1. A current flow controller comprising:
 a first current flow control sub-unit electrically connected to a first DC electrical network via a first input terminal, the first current flow control sub-unit comprising a first plurality of switches and a first energy storage device; 
 a second current flow control sub-unit electrically connected to the first DC electrical network via a second input terminal, the second current flow control sub-unit comprising a second plurality of switches and a second energy storage device, the second energy storage device electrically connected in parallel to the first energy storage device; 
 a first DC power transmission medium electrically connected in series to the first current flow control sub-unit via a first output terminal, the first DC power transmission medium further electrically coupled to a second DC electrical network; 
 a second DC power transmission medium electrically connected in series to the second current flow control sub-unit via a second output terminal, the second DC power transmission medium further electrically coupled to the second DC electrical network; 
 a switching control unit electrically connected to the first current flow control sub-unit, and electrically connected to the second current flow control sub-unit, the switching control unit controls a state of each of the first plurality of switches and each of the second plurality of switches to: 
 establish a first current flow away from the first DC power transmission medium by injecting a first non-zero voltage drop in series with the first DC power transmission medium; and 
 establish a second current flow toward the second DC power transmission medium by injecting a second non-zero voltage drop in series with the second DC power transmission medium; 
 thereby allowing energy to be transferred from the first DC power transmission medium to the second DC power transmission medium. 
 
     
     
       2. A current flow controller according to  claim 1  wherein the switching control unit controls the state of each of the first plurality of switches and each of the second plurality of switches such that currents in the first DC power transmission medium and the second DC power transmission medium are balanced. 
     
     
       3. A current flow controller according to  claim 1  wherein at least one of the first non-zero voltage drop and the second non-zero voltage drop is variable. 
     
     
       4. A current flow controller according to  claim 1  wherein at least one of the first non-zero voltage drop and the second non-zero voltage drop is a positive or negative DC voltage drop. 
     
     
       5. A current flow controller according to  claim 1  wherein at least one of the first current flow control sub-unit and the second current flow control sub-unit conducts current in two directions. 
     
     
       6. A current flow controller according to  claim 1  wherein at least one of the first plurality of switched and the second plurality of switches are connected in series. 
     
     
       7. A current flow controller according to  claim 1  wherein at least one of the first current flow control sub-unit and the second current flow control sub-unit includes a plurality of switching elements connected in parallel with an energy storage device in a full-bridge arrangement. 
     
     
       8. A current flow controller according to  claim 7  wherein the first current flow control sub-unit includes a plurality of first switching elements connected in parallel with the energy storage device in a full-bridge arrangement, and the second current flow control sub-unit includes a plurality of second switching elements connected in parallel with the same energy storage device in a full-bridge arrangement. 
     
     
       9. A current flow control circuit comprising:
 a first DC power transmission medium and a second DC power transmission medium for interconnecting a plurality of electrical elements; and 
 a current flow controller comprising:
 a first current flow control sub-unit electrically connected to a first DC electrical network via a first input terminal, the first current flow control sub-unit comprising a first plurality of switches and a first energy storage device; wherein the first DC power transmission medium is electrically connected to the first current flow control sub-unit via a first output terminal; 
 a second current flow control sub-unit electrically connected to the first DC electrical network via a second input terminal, the second current flow control sub-unit comprising a second plurality of switches and a second energy storage device, the second energy storage device electrically connected in parallel to the first energy storage device; wherein the second DC power transmission medium is electrically connected to the second current flow control sub-unit via a second output terminal; 
 a switching control unit electrically connected to the first current flow control sub-unit, and electrically connected to the second current flow control sub-unit, the switching control unit controls a state of each of the first plurality of switches and each of the second plurality of switches to: 
 establish a first current flow away from the first DC power transmission medium by injecting a first non-zero voltage drop in series with the first DC power transmission medium; and 
 establish a second current flow toward the second DC power transmission medium by injecting a second non-zero voltage drop in series with the second DC power transmission medium; 
 thereby allowing energy to be transferred from the first DC power transmission medium to the second DC power transmission medium. 
 
 
     
     
       10. A current flow control circuit according to  claim 9  wherein the switching control unit controls the state of each of the first plurality of switches and each of the second plurality of switches such that currents in the first DC power transmission medium and the second DC power transmission medium are balanced. 
     
     
       11. A current flow control circuit according to  claim 9  wherein at least one of the first current flow control sub-unit and the second current flow control sub-unit conducts current in two directions. 
     
     
       12. A current flow control circuit according to  claim 9  wherein at least one of the first plurality of switched and the second plurality of switches are connected in series. 
     
     
       13. A current flow control circuit according to  claim 9  wherein at least one of the first current flow control sub-unit and the second current flow control sub-unit includes a plurality of switching elements connected in parallel with an energy storage device in a full-bridge arrangement. 
     
     
       14. A current flow control circuit according to  claim 13  wherein the first current flow control sub-unit includes a plurality of first switching elements connected in parallel with the energy storage device in a full-bridge arrangement, and the second current flow control sub-unit includes a plurality of second switching elements connected in parallel with the same energy storage device in a full-bridge arrangement.